The present invention is related to centrifuge rotors and, more particularly, to test tube adapters to convert a single sample receiving cavity in the rotor to a multicavity configuration for receipt of a plurality of test tubes.
In the design of many presently used centrifuge rotors, such a swing bucket type rotor, the cavity for receiving the test sample is designed to be large to accommodate a large amount of the sample to be tested. However, at times it is desirable to utilize the same rotor to centrifuge smaller amounts of test samples in smaller cavities such as test tubes. Therefore, some type of an adapter is necessary to reduce the size of the rotor cavity to accommodate test tubes which can be located within the same large cavity. Typically the adapters which are currently utilized have a cylindrical configuration with an outer diameter substantially the same as the inner diameter of a rotor cavity. Within the adapter are a series of small diameter cavities or apertures for receipt of the test tubes carrying the various samples to be centrifuged. One end of the adapter is closed so that the bottoms of the test tubes rest within the adapter. In most instances the adapters have one specified depth. This becomes a problem when the adapter is a shorter depth than the test tubes, because the test tubes will not receive sufficient support during centrifugation. On the other hand, if the test tubes are shorter than the adapter, placement and removal of the test tubes within the adapter cavities is difficult. Further, when the adapter is shorter than the depth of the rotor cavity, as is typically the case, it is impossible to conveniently remove the adapter with the test tubes as a unit from the rotor, requiring the separate and tedious removal of each individual test tube from the rotor.
Typically the most economical way to produce the adapters is through injection molding. However, a significant disadvantage occurs with the utilization of injection molding when the adapter is of a significant depth, because the molding machine mold, carrying the core pins, requires a certain draft angle in order to allow the removal of the core pins subsequent to the injection molding process. Since a certain minimum diameter for each of the test tube cavities must be present throughout the depth of the adapter, a sizable difference can accumulate between the minimum diameter of the test tube cavity at the bottom of the adapter and the diameter of the cavity at the open or upper end of the adapter. The accumulation of the draft angle can be significant enough to sacrifice the necessary support around the test tube or force a decrease in the number of cavities in a given diameter adapter. When such draft angle accumulation is not tolerable, the user in many instances is forced to custom drill the test tube cavities from a solid cylindrical member to provide a more uniform test tube cavity throughout the depth of the adapter. This becomes very expensive when producing several adapters because of the drilling work.
A further problem related to the injection molding of adapters of a significant depth is related to the drift which occurs in some cases with core pins in the mandrel resulting in some of the test tube cavities being improperly spaced and not having sufficient spacing between each other to establish a satisfactory wall between the tube cavities.
Another inherent disadvantage to the presently used adapters relates to the bottom support for the test tube within the adapter. Since the adapter is typically made of a rigid material and has a closed bottom, it is necessary to put some type of cushioning material in the bottom of each of the test tube cavities. Such approach presently uses the tedious method of inserting a cushioning pad at the bottom of each of the test tube cavities to provide the necessary support of the test tube. However, during centrifugation, the cushioning pads do not provide the necessary support, resulting in the test tube having a single point of contact with the bottom hard surface of the adapter. This lessens the maximum load which the test tube can withstand during centrifugation.